Atrial fibrillation in cows: clinical findings and therapeutic considerations.

In a 3-year period, atrial fibrillation (AF) was diagnosed in 16 dairy cows between the ages of 2 and 11 years. Ten cows had AF when they were referred to the hospital and 6 cows developed AF while hospitalized. The chief reason for hospitalization in 15 of the cows was a gastrointestinal problem. Characteristic auscultatory findings were irregular rhythm (mean rate +/- SD: 94 +/- 25 beats/min), variation in the intensity of heart sounds, and absence of the 4th heart sound. The electrocardiographic features of AF were ventricular and F wave (mean +/- SD) rates of 94.4 +/- 24.8 and 272.7 +/- 53.3 beats/min, respectively. The most common electrolyte disorders were hypocalcemia, hypochloremia, and hypokalemia. Some of the cows had no acid-base imbalance, but metabolic alkalosis, respiratory alkalosis, and metabolic acidosis were found in other cows. Conversion to normal sinus rhythm (NSR) without specific therapy was documented by electrocardiography in 6 cows. In 7 of 9 cows treated with quinidine sulphate or quinidine gluconate, the AF converted to NSR. Quinidine plasma concentration at the time of conversion ranged from 2.2 to 24 micrograms/ml. Four cows died while they were hospitalized. Only 1 cow was in AF at the time of death and in no case was death attributed to AF. A follow-up on each of the survivors indicated that the persistence of AF was associated with poor performance and progressive cardiac disease, whereas conversion to NSR uniformly led to clinical improvement.